The latest addition to my collection is this Howard Grubb aluminium Aplanatic 12x10 lens made in Dublin, probably in the late 1890s. This was probably one of the earliest aluminium lenses made by Grubb. Were there aluminium lenses from other manufacturers before this time? Aluminium was lighter than brass, but was then new as a refined product for manufacturing and very expensive to produce.
The lens has a diaphragm aperture, shown below at f22.
The lens has an aperture scale showing f11.3, 16, 22, 32, 45 and 64. F 11.3 was used in the Royal Photographic Society aperture scale which was introduced between 1895 and 1902. Any information about the date of introduction of the RPS scale might help to date the lens. I have access to a works notebook which provides finish dates for various Grubb lenses made in Dublin, but it ends before this serial number.
This might point to a specialised application which could have been for astronomical, scientific, industrial or military purposes. Meteorological use has also been suggested as the orange would enhance cloud formations. The Grubb works had also produced astronomical instruments for many years before this lens was made and was also getting involved in the manufacture of military optics around this time.
There is no sign of the signature on the edge of the lens which was there in the time of Howard's father, Thomas Grubb. This was mentioned in a previous blog post.
All helpful suggestions would be gratefully received.
Finally, the real mystery. The lens itself is orange coated, just like an orange filter for enhancing contrast.